To improve the performance of four cycle internal combustion engines, it has been proposed to incorporate a reed valve in the induction passage of each cylinder in series with the intake poppet valve. The benefits of such reed valves include the ability to broaden the torque range of the engine (by producing higher torque at lower engine speeds with limited effect on high speed power), improving idle quality, and reducing light load fuel consumption. The reed valves generally have a cantilever beam design which can cause a pressure drop and an associated loss in flow which can result in loss of power and/or efficiency under certain engine operating conditions. Also, the continuous flexing of the reed petal can limit its fatigue life. Moreover, a reed petal structure able to withstand large pressures downstream of it can limit the engine performance improvements resulting from the reed valve, and increase the cost of the reed valve.
To obtain the advantages resulting from reed valves, an alternative approach is to use variable valve timing This requires the lift, timing, and/or duration of the intake and/or exhaust valves to be changed based on engine operating conditions and comprises manipulation of the actual valve train which can involve relatively high forces and loads on the valve train. Designs to accomplish such operations can lead to high levels of cost and complexity. Further, to obtain all the benefits of a reed valve induction system, the variable valve timing system must vary both the duration and phasing of the intake valve opening which presents a technological challenge.
Rotary valves in induction systems can be used alone or in series with conventional poppet valves to offer adjustability to the intake control. A rotary valve in the intake manifold may be driven by the engine to permit periodic flow in phase with the periodic intake flow into the respective cylinder. In place of the standard poppet valve, an axially shiftable rotary valve with shaped ports can be used to vary the duration of the rotary valve opening. Also, a rotary valve can be driven from the crankshaft in phase with the crankshaft, with the phase being adjustable according to load conditions. Furthermore, instead of a poppet valve, an axially shiftable rotary valve with a valve port tapered in a manner to change both the phase and duration of the rotary valve opening upon axial shifting can be used. The amount of phase shift relative to the amount of duration change is fixed according to the valve port design so that the phase and duration are interdependent.